The present invention relates to a photographic printer in which a CRT is used as a light source for making a print from a photographic film and, more particularly, to a photographic printer which is capable of correcting shading of an image of a print.
General photographic printers, which use halogen lamps as a light source, is provided with a diffusion box disposed between a halogen lamp and film deck for holding a photographic film, for example a color negative film, so as to illuminate a negative image with a light sufficiently mixed by the diffusion box in order to print the negative image onto a photographic material, for example a color photographic paper, by a printing lens. There is also known (for example in Japanese patent publication No. 45-5336) a photographic printer uses a CRT as a light source since, although an exposure time becomes long, a gradation correction is effected easily.
In those photographic printers, a negative image is, even though illuminated with an uniform light, sometimes not finished as a favorable print due an effect of shading. There are two types of shadings; one occuring upon taking a photograph and the other occuring upon photographic printing.
The former shading is due to an insufficient amount of light passing through the edge of a taking lens and an insufficient amount of light emitted from marginal portion of a strobe. These shadings are significantly produced when compact cameras with built-in strobe is used. And these shadings, which are recorded on negatives, are different in degree depending on negative images. The later shading is due to an insufficient amount of light produced by a printing and an unevenness of light emitted from a light source. These shadings are always constant when a same printing lens is used.
Conventional photographic printers described above cannot correct shadings appeared on negative images due to taking lenses and/or strobes used. On the other hand, in the conventional photographic printers, shadings occurring due to the characteristics of printing lenses are corrected by the use of shading correcting optical systems such as parabola shading lenses or shading correcting plates. However, shadings change depending on the kinds of printing optical lenses, it is necessary to replace such shading correcting optical systems upon changing printing lenses to be used. This is a quite troublesome operation.